Technical field
The invention relates to real-time processing of an electroencephalographic signal, generally called an EEG signal, with a view to automatic classification of a patient's sleep stages from the characteristics of the EEG signal. It has important, although not exclusive, applications in sleep studies in hospital laboratories, and in studying changes in sleeping patterns under drugs in pharmaceutical laboratories.
EEG specialists usually recognize six different stages, and the signals obtained in, successive time segments are allocated to one of the six stages.
At the present time, the successive sleep stages of a patient are determined by visually analyzing an EEG graph and that requires two to three days of work for each graph for one night of sleep, with a match of about 80% between the results obtained by different operators. This method of analysis is laborious and very slow. For each signal segment, the operator must make a frequency analysis by observing a time signal, implying considerable smoothing and subjective evaluation, which has led to the classification into six stages only, usually called waking, paradoxical sleep, stage 1, stage 2, stage 3, and stage 4.
A system has been proposed comprising a microcomputer which determines the sleep stages by analyzing signals from various leads of an electroencephalograph. The signals, sampled at a high frequency (1000 Hz for processing signals having a maximum frequency of 30 Hz) and digitized, are applied to a bank of digital filters with fixed characteristic frequencies. This device transposes visual analysis and does not improve the performance thereof.